I have had some success converting EAD and MARC into RDF/XML, and consequently I am able to literally illustrate the resulting RDF triples.
I have acquired sets of EAD files and MARC records of an archival nature. When it comes to EAD files I am able to convert them into RDF/XML with a stylesheet from the Archives Hub. I then fed the resulting RDF/XML to the W3C RDF Validation Service and literally got an illustration of the RDF, below:
Transforming MARC into RDF was a bit more complicated. I first convert a raw MARC record into MARCXML with a Perl module called MARC::File::XML. I transformed the result into MODS with MARC21slim2MODS3.xsl, and finally into RDF/XML with mods2rdf.xslt. Again, I validated the results to got the following illustration:
The resulting images are huge, and the astute/diligent reader will see a preponderance of literals in the results. This is not a good thing, but it all that is available right now.
On the other hand the same astute/diligent reader will see the root of the RDF/XML pointing to a meaningful URI. This URI will be resolvable in the near future via content negotiation. This is a simple first step. The next steps will be to apply this process to an entire collection of EAD files and MARC records. After that the two other things can happen: 1) the original metadata files can begin to include URIs, and 2) the XSL used to process the metadata can employ a more standardized ontology. It is not an easy process, but it is a beginning.
Right now, something is better than nothing.